Catalyst for Producing Acrylic Acids and Acrylates

ABSTRACT

The invention is to a process for producing an acrylate product. The process includes the steps of contacting an alkanoic acid and an alkylenating agent over a catalyst composition under conditions effective to produce the acrylate product. The catalyst composition comprises vanadium, titanium and tungsten. Preferably, the catalyst comprises vanadium to tungsten at a molar ratio of at least 0.02:1, in an active phase.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/610,104, filed on Mar. 13, 2012, the entire contents and disclosuresof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to the production of acrylicacid. More specifically, the present invention relates to a catalyst foruse in the production of acrylic acid via the aldol condensation ofacetic acid and formaldehyde.

BACKGROUND OF THE INVENTION

α,β-unsaturated acids, particularly acrylic acid and methacrylic acid,and the ester derivatives thereof are useful organic compounds in thechemical industry. These acids and esters are known to readilypolymerize or co-polymerize to form homopolymers or copolymers. Oftenthe polymerized acids are useful in applications such assuperabsorbents, dispersants, flocculants, and thickeners. Thepolymerized ester derivatives are used in coatings (including latexpaints), textiles, adhesives, plastics, fibers, and synthetic resins.

Because acrylic acid and its esters have long been valued commercially,many methods of production have been developed. One exemplary acrylicacid ester production process involves the reaction of acetylene withwater and carbon monoxide. Another conventional process involves thereaction of ketene (often obtained by the pyrolysis of acetone or aceticacid) with formaldehyde. These processes have become obsolete foreconomic, environmental, or other reasons.

Another acrylic acid production method utilizes the condensation offormaldehyde and acetic acid and/or carboxylic acid esters. Thisreaction is often conducted over a catalyst. For example, condensationcatalyst consisting of mixed oxides of vanadium, titanium, and/orphosphorus were investigated and described in M. Ai, J. Catal., 107, 201(1987); M. Ai, J. Catal., 124, 293 (1990); M. Ai, Appl. Catal., 36, 221(1988); and M. Ai, Shokubai, 29, 522 (1987). These catalysts have avanadium:titanium:phosphorus molar ratio of 1:2:x, where x is variedfrom 4.0 to 7.0, and have traditionally shown that the catalyst activitydecreases steadily as the phosphorus content increased. The highestselectivity with respect to the aldol condensation products, e.g.,acrylic acid and methyl acrylate, was obtained where x was 6.0. Withthese catalysts, the molar ratio of vanadium to titanium was maintainedat or below 1:2. The acetic acid conversions achieved using thesecatalysts, however, leave room for improvement.

Heteropolyacid catalysts comprising bismuth have also been studied. U.S.Pat. No. 7,851,397 teaches the use of a heteropolyacid catalyst foroxidizing unsaturated and/or saturated aldehydes, such as acrolein ormethacrolein, to unsaturated acids, such as acrylic acid or methacrylicacid. The catalyst contains molybdenum, phosphorus, vanadium, bismuthand a first component selected from the group consisting of potassium,rubidium, cesium, thallium and a mixture thereof. The methods for makingthese heteropolyacid catalysts are cumbersome as they involve theaddition of each metal solution individually to an ammoniumparamolybdate solution.

Even in view of these references, the need exists for improved processesfor producing acrylic acid, and for an improved catalyst capable ofproviding high acetic acid conversions and acrylate product yields.

SUMMARY OF THE INVENTION

In one embodiment, the present invention relates to a catalystcomposition suitable for use in an aldol condensation of an alkanoicacid and an alkylenating agent to form an acrylate product. The catalystcomposition comprises an active phase comprising: vanadium, titanium,and tungsten. Preferably, these components are present in a molar ratioof vanadium to tungsten in the active phase of the catalyst compositionof at least 0.02:1. In another embodiment, the molar ratio of vanadiumto tungsten in the active phase of the catalyst composition ranges from0.02:1 to 1000:1.

In another embodiment, the present invention relates to a process forproducing an acrylate product, the process comprising the steps of: (a)contacting an alkanoic acid and an alkylenating agent over theabove-identified catalyst under conditions effective to produce theacrylate product. Preferably, the alkylenating agent is formaldehyde,the alkanoic acid is acetic acid, and the acrylate product is acrylicacid. In one embodiment the overall alkanoic acid conversion in thereaction is at least 15 mol %, acrylic acid selectivity of at least 30%,and the space time yield of acrylate product is at least 50 grams perliter of catalyst per hour.

In another embodiment, the invention is to a process for producing theabove-identified catalyst. The process comprises the steps of: (a)contacting a titanium precursor, a vanadium precursor, and a tungstenprecursor to form a wet catalyst precursor mixture, and (b) drying thewet catalyst precursor mixture to form a dried catalyst compositioncomprising titanium, vanadium, and tungsten. The process may furthercomprise the step of mixing a vanadium precursor and a reductantsolution to form a vanadium precursor solution. The contacting step maycomprise the step of contacting a binder with the titanium precursor,the tungsten precursor, and/or the vanadium precursor solution to form awet catalyst composition.

DETAILED DESCRIPTION OF THE INVENTION Introduction

Production of unsaturated carboxylic acids such as acrylic acid andmethacrylic acid and the ester derivatives thereof via most conventionalprocesses have been limited by economic and environmental constraints.One of the more practical processes for producing these acids and estersinvolves the aldol condensation of formaldehyde and (i) acetic acidand/or (ii) ethyl acetate over a catalyst. Exemplary classes ofconventional catalyst include binary vanadium-titanium phosphates,vanadium-silica-phosphates, and alkali metal-promoted silicas, e.g.,cesium- or potassium-promoted silicas. The alkali metal-promotedsilicas, however, have been known to exhibit only low to moderateactivity when used in aldol condensation reactions.

It has now been discovered that certain catalysts effectively catalyzethe aldol condensation of a carboxylic acid with an alkylenating agent,e.g. a methylenating agent, such as formaldehyde to form an unsaturatedacid. Preferably, the reaction is an aldol condensation reaction ofacetic acid with formaldehyde to form acrylate product(s), e.g., acrylicacid.

Accordingly, in one embodiment, the present invention relates to acatalyst composition suitable for use in an aldol condensation of aceticacid and formaldehyde. The catalyst composition comprises vanadium,titanium, and tungsten. Surprisingly and unexpectedly, thevanadium-titanium-tungsten catalyst provides high conversions,selectivities, and yields, as compared to conventional catalysts.

In one embodiment, the present invention is to a process for producingacrylic acid, methacrylic acid, and/or the salts and esters thereof. Asused herein, acrylic acid, methacrylic acid, and/or the salts and estersthereof, collectively or individually, may be referred to as “acrylateproduct” or “acrylate products.” The use of the terms acrylic acid,methacrylic acid, or the salts and esters thereof, individually, doesnot exclude the other acrylate products, and the use of the termacrylate product does not require the presence of acrylic acid,methacrylic acid, and the salts and esters thereof.

The inventive catalyst composition also shows a low deactivation rateand provides stable performance for the aldol condensation reaction overa long period of time, e.g., over 5 hours, over 10 hours, over 20 hours,or over 50 hours.

In one embodiment, the vanadium, titanium and tungsten are presenteither in the elemental form or as a respective oxide or phosphate. Thecatalyst composition may comprise an active phase, which comprises thecomponents that promote the catalysis, and may also comprise a supportor a modified support. As one example, the active phase comprisesmetals, phosphorus-containing compounds, and oxygen-containingcompounds. In a preferred embodiment, vanadium, titanium, and tungstenare present in the active phase. Preferably, the molar ratio of vanadiumto tungsten in the active phase of the catalyst composition is greaterthan 0.02:1, e.g., greater than 0.05:1, greater than 0.10:1, greaterthan 1:1, greater than 7:1, greater than 10:1, or greater than 30:1, orgreater than 62.5:1. In terms of ranges, the molar ratio of vanadium totungsten in the inventive catalyst may range from 0.02:1 to 1000:1,e.g., from 0.05:1 to 250:1, from 0.10:1 to 150:1, or from 2:1 to 62.5:1.In an embodiment, the molar ratio of vanadium to titanium in the activephase of the catalyst composition is greater than 0.02:1, e.g., greaterthan 0.05:1, greater than 0.10:1, greater than 0.44:1, greater than 1:1,greater than 10:1, or greater than 30:1. In terms of ranges, the molarratio of vanadium to titanium in the inventive catalyst may range from0.02:1 to 1000:1, e.g., from 0.05:1 to 500:1, from 0.10:1 to 150:1, from0.40:1 to 62.5:1.

The inventive catalyst has been found to achieve unexpectedly highacetic acid conversions. For example, depending on the temperature atwhich the acrylic acid formation reaction is conducted, acetic acidconversions of at least 15 mol %, e.g., at least 25 mol %, at least 30mol %, e.g., at least 40 mol %, or at least 50 mol %, may be achievedwith this catalyst composition. This increase in acetic acid conversionis achieved while maintaining high selectivity to the desired acrylateproduct such as acrylic acid or methyl acrylate. For example,selectivities to the desired acrylate product of at least 35 mol %,e.g., at least 45 mol %, at least 60 mol %, or at least 70 mol % may beachieved with the catalyst composition of the present invention.

The total amounts of vanadium, titanium and tungsten in the catalystcomposition of the invention may vary widely. In some embodiments, forexample, the catalyst composition comprises at least 0.2 wt % vanadium,e.g., at least 1.0 wt %, at least 6 wt %, at least 10 wt %, or at least27 wt. % based on the total weight of the active phase of the catalystcomposition. The catalyst composition may comprise in the active phaseat least 0.016 wt % titanium, e.g., at least 0.24 wt %, at least 1 wt %,at least 8 wt %, or at least 13 wt %. The catalyst composition maycomprise in the active phase at least 0.11 wt % tungsten, e.g., at least0.4 wt %, at least 0.6 wt %, at least 2 wt %, at least 5 wt % or atleast 9 wt %. In terms of ranges, the catalyst composition may comprisein the active phase from 0.2 wt % to 35 wt % vanadium, e.g., from 0.5 wt% to 29 wt %, from 1 wt % to 28 wt %, or from 6 wt % to 28 wt %; from0.016 wt % to 25 wt % titanium, e.g., from 0.24 wt % to 25 wt %, from0.27 wt % to 14 wt %, from 0.9 wt % to 19 wt %; and 0.11 wt % to 65 wt %tungsten, e.g., from 0.21 wt % to 63 wt %, from 0.4 wt % to 58 wt %, orfrom 0.6 wt % to 10 wt %. The catalyst composition may comprise at most35 wt % vanadium, e.g., at most 28 wt % or at most 20 wt %. The catalystcomposition may comprise in the active phase at most 25 wt % titanium,e.g., at most 19 wt % or at most 18 wt %. The catalyst composition maycomprise in the active phase at most 65 wt % tungsten, e.g., at most 63wt % or at most 58 wt %.

In one embodiment, the catalyst comprises in the active phase vanadiumand titanium, in combination, in an amount at least 0.4 wt %, e.g., atleast 3 wt %, at least 10 wt %, at least 15 wt %, at least 18 wt %, atleast 20 wt %, or at least 29 wt %. In terms of ranges, the combinedweight percentage of the vanadium and titanium components in the activephase may range from 0.4 wt % to 30 wt %, e.g., from 1.3 wt % to 30 wt%, from 3 wt % to 29 wt %, or from 18 wt % to 30 wt %. In oneembodiment, the catalyst comprises in the active phase vanadium andtungsten, in combination, in an amount at least 0.58 wt %, e.g., atleast 3 wt %, at least 9 wt %, at least 15 wt %, at least 25 wt %, or atleast 33 wt %. In terms of ranges, the combined weight percentage ofvanadium and tungsten in the active phase may range from 0.58 wt % to 65wt %, e.g., from 1.4 wt % to 63 wt %, from 2.7 wt % to 5.9 wt %, or from9 wt % to 34 wt %. In one embodiment, the catalyst comprises in theactive phase vanadium, titanium and tungsten, in combination, in anamount at least 20 wt %, e.g., at least 23 wt %, at least 28 wt %, atleast 33 wt %, or at least 38 wt %. In terms of ranges, the combinedweight percentage of the vanadium, titanium and tungsten components inthe active phase may range from 20 wt % to 65 wt %, e.g., from 21 wt %to 64 wt %, from 22 wt % to 61 wt %, or from 23 wt % to 39 wt %.

In other embodiments, the inventive catalyst may further comprise othercompounds or elements (metals and/or non-metals). For example, thecatalyst may further comprise phosphorus and/or oxygen. In these cases,the catalyst may comprise from 12 wt % to 21 wt % phosphorus, e.g., from13 wt % to 28 wt % or from 14 wt % to 28 wt %; and/or from 22 wt % to 51wt % oxygen, e.g., from 23 wt % to 51 wt % or from 26 wt % to 51 wt %.

In some embodiments, the tungsten is present in the form of a tungstensalt. For example, the catalyst composition may comprise the tungstensalt in an amount ranging from 0.1 wt % to 65 wt %, e.g., from 0.21 wt %to 63 wt % or from 0.4 wt % to 58 wt %. Preferably the tungsten saltused in the preparation of the inventive catalyst is tungsten (VI) salt.The tungsten salt may for instance be selected from tungstic acid,silicotungstic acid, ammonium silicotungstic acid, ammoniummetatungstate hydrate, ammonium paratungstate, ammoniumtetrathiotungstate, hydrogentungstate, polymer-supported,bis(tert-butylimino)bis(dimethylamino)tungsten(VI), phosphotungstic acidhydrate, piperidine tetrathiotungstate, tungsten(VI) chloride,tungsten(VI) dichloride dioxide, tungsten(VI) fluoride, tungsten(IV)oxide, tungsten(VI) oxychloride, tungstosilicic acid hydrate.

In one embodiment, the formation of the catalyst composition may utilizethe reduction of a pentavalent vanadium compound. The reducedpentavalent compound may be combined with a phosphorus compound and,optionally, promoters under conditions effective to provide or maintainthe vanadium in a valence state below +5 to form the active metalphosphate catalysts. Various reducing agents and solvents may be used toprepare these catalysts. Examples include organic acids, alcohols,polyols, aldehydes, and hydrochloric acid. Generally speaking, thechoice of the metal precursors, reducing agents, solvents, sequence ofaddition, reaction conditions such as temperature and times, andcalcination temperatures may impact the catalyst composition, surfacearea, porosity, structural strength, and overall catalyst performance.

In one embodiment, suitable vanadium compounds that serve as a source ofvanadium in the catalyst composition contain pentavalent vanadium andinclude, but are not limited to, vanadium pentoxide or vanadium saltssuch as ammonium metavanadate, vanadium oxytrihalides, vanadiumalkylcarboxylates and mixtures thereof.

In some embodiments, the titanium is present in compound form such as inthe form of titanium dioxide. For example, the catalyst may comprisetitanium dioxide in an amount ranging from 0.1 wt % to 95 wt %, e.g.,from 5 wt % to 50 wt % or from 7 wt % to 25 wt %. In these cases, thetitanium dioxide may be in the rutile and/or anatase form, with theanatase form being preferred. If present, the catalyst preferablycomprises at least 5 wt % anatase titanium dioxide, e.g., at least 10 wt% anatase titanium dioxide, or at least 50 wt % anatase titaniumdioxide. Preferably less than 20 wt % of the titanium dioxide, ifpresent in the catalyst, is in rutile form, e.g., less than 10 wt % orless than 5 wt %. In other embodiments, the catalyst comprises anatasetitanium dioxide in an amount of at least 5 wt %, e.g., at least 10 wt %or at least 20 wt %. In another embodiment, the titanium is present inthe form of amorphous titanium hydroxide gel, which is preferablyconverted to TiP₂O₇.

The titanium hydroxide gel may be prepared by any suitable meansincluding, but not limited to, the hydrolysis of titanium alkoxides,substituted titanium alkoxides, or titanium halides. In otherembodiments, colloidal titania sols and/or dispersions may be employed.In one embodiment, titania coated colloidal particles or supports areused as a source of titanium dioxide. The hydrous titania may beamorphous or may contain portions of anatase and/or rutile depending onpreparation method and heat treatment.

Upon treatment with a phosphating agent, the various forms of titaniamay be converted to titanium phosphates and/or titanium pyrophosphates.In some cases, a portion of the titanium may be present as unconvertedtitania and, hence, will be present in the final catalyst as anatase orrutile forms.

Generally speaking, the proportion of the crystalline forms of titaniapresent in the catalyst is dependent on the titanium precursor, thepreparative method, and/or the post-phosphorylating treatment. In oneembodiment, the amount of anatase and rutile present in the active phaseof the catalyst is minimized. The amount of crystalline titania,however, may be high with only a thin shell of porous catalyst existingon the titania support.

In one embodiment, suitable phosphorus compounds that serve as a sourceof phosphorus in the catalyst contain pentavalent phosphorus andinclude, but are not limited to, phosphoric acid, phosphorus pentoxide,polyphosphoric acid, or phosphorus perhalides such as phosphoruspentachloride, and mixtures thereof.

In one embodiment, the active phase of the catalyst corresponds to theformula:

V_(a)Ti_(b)W_(c)P_(d)O_(e)

wherein:a is from 1 to 100,b is from 0.1 to 50,c is from 0.1 to 50,d is from 1 to 270,e is from 6 to 1040.

The letters a, b, c, d and e are the relative molar amounts (relative to1.0) of vanadium, titanium, tungsten, phosphorus and oxygen,respectively in the catalyst. In these embodiments, the ratio of a to bis greater than 0.02:1, e.g., greater than 0.05:1, greater than 0.10:1,greater than 1:1, or greater than 2:1. Preferred ranges for molarvariables a, b, c, d and e are shown in Table 1.

TABLE 1 Molar Ranges Molar Range Molar Range Molar Range a 1 to 100 1 to25 1 to 15 b 0.1 to 50   0.1 to 20  0.1 to 10  c 0.1 to 50   0.1 to 20 0.1 to 10  d 1 to 270 2 to 91 3 to 50 e  6 to 1040  9 to 344 13 to 184

In some embodiments, the catalyst composition further comprisesadditional metals and/or metal oxides. These additional metals and/ormetal oxides may function as promoters. If present, the additionalmetals and/or metal oxides may be selected from the group consisting ofcopper, molybdenum, nickel, niobium, and combinations thereof. Otherexemplary promoters that may be included in the catalyst of theinvention include lithium, sodium, magnesium, aluminum, chromium,manganese, iron, cobalt, calcium, yttrium, ruthenium, silver, tin,barium, lanthanum, the rare earth metals, hafnium, tantalum, rhenium,thorium, bismuth, antimony, germanium, zirconium, uranium, cesium, zinc,and silicon and mixtures thereof. Other modifiers include boron,gallium, arsenic, sulfur, halides, Lewis acids such as BF₃, ZnBr₂, andSnCl₄. Exemplary processes for incorporating promoters into catalyst aredescribed in U.S. Pat. No. 5,364,824, the entirety of which isincorporated herein by reference.

If the catalyst composition comprises additional metal(s) and/or metaloxides(s), the catalyst optionally may comprise in active phaseadditional metals and/or metal oxides in an amount from 0.001 wt % to 30wt %, e.g., from 0.01 wt % to 5 wt % or from 0.1 wt % to 5 wt %. Ifpresent, the promoters may enable the catalyst to have a weight/weightspace time yield of at least 25 grams of acrylic acid/gram catalyst-h,e.g., at least 50 grams of acrylic acid/gram catalyst-h, or at least 100grams of acrylic acid/gram catalyst-h.

In some embodiments, the catalyst composition is unsupported. In thesecases, the catalyst may comprise a homogeneous mixture or aheterogeneous mixture as described above. In one embodiment, thehomogeneous mixture is the product of an intimate mixture of vanadium,titanium and tungsten resulting from preparative methods such ascontrolled hydrolysis of metal alkoxides or metal complexes. In otherembodiments, the heterogeneous mixture is the product of a physicalmixture of the vanadium, titanium salt and tungsten salt. These mixturesmay include formulations prepared from phosphorylating a physicalmixture of preformed hydrous metal oxides. In other cases, themixture(s) may include a mixture of preformed vanadium pyrophosphate andtitanium pyrophosphate powders.

In another embodiment, the catalyst composition is a supported catalystcomprising a catalyst support in addition to the vanadium, titanium andtungsten and optionally phosphorous and oxygen, in the amounts indicatedabove (wherein the molar ranges indicated are without regard to themoles of catalyst support, including any vanadium, titanium, phosphorousor oxygen contained in the catalyst support). The total weight of thesupport (or modified support), based on the total weight of thecatalyst, preferably is from 25 wt % to 95 wt %, e.g., from 40 wt % to70 wt % or from 50 wt % to 60 wt %, and the total weight of the activephase is from 0.1 wt % to 25 wt %, based on the total weight of thecatalyst composition. In a preferred embodiment, the weight of theactive phase is at least 6 wt % of the total catalyst compositionweight.

The support may vary widely. In one embodiment, the support material isselected from the group consisting of silica, alumina, zirconia,titania, aluminosilicates, zeolitic materials, mixed metal oxides(including but not limited to binary oxides such as SiO₂—Al₂O₃,SiO₂—TiO₂, SiO₂—ZnO, SiO₂—MgO, SiO₂—ZrO₂, Al₂O₃—MgO, Al₂O₃—TiO₂,Al₂O₃—ZnO, TiO₂—MgO, TiO₂—ZrO₂, TiO₂—ZnO, TiO₂—SnO₂) and mixturesthereof, with silica being one preferred support. Other suitable supportmaterials may include, for example, stable metal oxide-based supports orceramic-based supports. Preferred supports include silicaceous supports,such as silica, silica/alumina, a Group IIA silicate such as calciummetasilicate, pyrogenic silica, high purity silica, silicon carbide,sheet silicates or clay minerals such as montmorillonite, beidellite,saponite, pillared clays, and mixtures thereof. Other supports mayinclude, but are not limited to, iron oxide, magnesia, steatite,magnesium oxide, carbon, graphite, high surface area graphitized carbon,activated carbons, and mixtures thereof. Other supports may includecoated structured forms such as coated metal foil, sintered metal formsand coated ceramic formed shapes such as shaped cordierite, platyalumina or acicular mullite forms. These listings of supports are merelyexemplary and are not meant to limit the scope of the present invention.

In other embodiments, in addition to the active phase and a support, theinventive catalyst may further comprise a support modifier. A modifiedsupport, in one embodiment, relates to a support that includes a supportmaterial and a support modifier, which, for example, may adjust thechemical or physical properties of the support material such as theacidity or basicity of the support material. In embodiments that use amodified support, the support modifier is present in an amount from 0.1wt % to 50 wt %, e.g., from 0.2 wt % to 25 wt %, from 0.5 wt % to 15 wt%, or from 1 wt % to 8 wt %, based on the total weight of the catalystcomposition.

In one embodiment, the support modifier is an acidic support modifier.In some embodiments, the catalyst support is modified with an acidicsupport modifier. The support modifier similarly may be an acidicmodifier that has a low volatility or little volatility. The acidicmodifiers may be selected from the group consisting of oxides of GroupIVB metals, oxides of Group VB metals, oxides of Group VIB metals, ironoxides, aluminum oxides, and mixtures thereof. In one embodiment, theacidic modifier may be selected from the group consisting of WO₃, MoO₃,Fe₂O₃, Cr₂O₃, V₂O₅, MnO₂, CuO, Co₂O₃, Bi₂O₃, TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃.

In another embodiment, the support modifier is a basic support modifier.The presence of chemical species such as alkali and alkaline earthmetals, are normally considered basic and may conventionally beconsidered detrimental to catalyst performance. The presence of thesespecies, however, surprisingly and unexpectedly, may be beneficial tothe catalyst performance. In some embodiments, these species may act ascatalyst promoters or a necessary part of the acidic catalyst structuresuch in layered or sheet silicates such as montmorillonite. Withoutbeing bound by theory, it is postulated that these cations create astrong dipole with species that create acidity.

Additional modifiers that may be included in the catalyst include, forexample, boron, aluminum, magnesium, zirconium, and hafnium.

In some embodiments, the support may be a support having a surface areaof at least 1 m²/g, e.g., at least 20 m²/g or at least 50 m²/g, asdetermined by BET measurements. The catalyst support may include pores,optionally having an average pore diameter ranging from 5 nm to 200 nm,e.g., from 5 nm to 50 nm or from 10 nm to 25 nm. The catalyst optionallyhas an average pore volume of from 0.05 cm³/g to 3 cm³/g, e.g., from0.05 cm³/g to 0.1 cm³/g or from 0.08 cm³/g to 0.1 cm³/g, as determinedby BET measurements. Preferably, at least 50% of the pore volume orsurface area, e.g., at least 70% or at least 80%, is provided by poreshaving the diameters discussed above. Pores may be formed and/ormodified by pore modification agents, which are discussed below. Inanother embodiment, the ratio of microporosity to macroporosity rangesfrom 19:1 to 5.67:1, e.g., from 3:1 to 2.33:1. Microporosity refers topores smaller than 2 nm in diameter, and movement in micropores may bedescribed by activated diffusion. Mesoporosity refers to pores greaterthan 2 nm and less than 50 nm is diameter. Flow through mesopores may bedescribed by Knudson diffusion. Macroporosity refers to pores greaterthan 50 nm in diameter and flow though macropores may be described bybulk diffusion. Thus, in some embodiments, it is desirable to balancethe surface area, pore size distribution, catalyst or support particlesize and shape, and rates of reaction with the rate of diffusion of thereactant and products in and out of the pores to optimize catalyticperformance.

As will be appreciated by those of ordinary skill in the art, thesupport materials, if included in the catalyst of the present invention,preferably are selected such that the catalyst system is suitablyactive, selective and robust under the process conditions employed forthe formation of the desired product, e.g., acrylic acid or alkylacrylate. Also, the active metals that are included in the catalyst ofthe invention may be dispersed throughout the support, coated on theouter surface of the support (egg shell) or decorated on the surface ofthe support. In some embodiments, in the case of macro- and meso-porousmaterials, the active sites may be anchored or applied to the surfacesof the pores that are distributed throughout the particle and hence aresurface sites available to the reactants but are distributed throughoutthe support particle.

The inventive catalyst may further comprise other additives, examples ofwhich may include: molding assistants for enhancing moldability;reinforcements for enhancing the strength of the catalyst; pore-formingor pore modification agents for formation of appropriate pores in thecatalyst, and binders. Examples of these other additives include stearicacid, graphite, starch, methyl cellulose, silica, alumina, glass fibers,silicon carbide, and silicon nitride. In one embodiment, the activephase of the catalyst (not the support) comprises the other additives.For example, the active phase may comprise silica, e.g., colloidalsilica. In such embodiments, the silica may be present in the activephase in amounts ranging from 0.01 to 50 wt % silica, e.g., from 0.1 wt% to 40 wt %, from 0.5 wt % to 30 wt %, from 1.0 wt % to 30 wt %, from 2wt % to 15 wt %, or from 2 wt % to 9 wt %. In terms of lower limits, theactive phase may comprise at least 0.01 wt % silica, e.g., at least 0.1wt %, at least 0.5 wt %, or at least 1 wt %. In terms of upper limits,the active phase may comprise less than 50 wt % silica, e.g., less than40 wt %, less than 30 wt %, or less than 20 wt %. Preferably, theseadditives do not have detrimental effects on the catalytic performances,e.g., conversion and/or activity. These various additives may be addedin such an amount that the physical strength of the catalyst does notreadily deteriorate to such an extent that it becomes impossible to usethe catalyst practically as an industrial catalyst.

In one embodiment, the inventive catalyst composition comprises a poremodification agent. In some embodiments, the pore modification agent maybe thermally stable and has a substantial vapor pressure at atemperature below 300° C., e.g., below 250° C. In one embodiment, thepore modification agent has a vapor pressure of at least 0.1 kPa, e.g.,at least 0.5 kPa, at a temperature between about 150° C. and about 250°C., e.g., between about 150° C. and about 200° C. In other embodiments,pore modification agent may be thermally decomposed or burned out tocreate pores. For example, the burned out agent may be cellulose-derivedmaterials such as ground nut shells.

In some embodiments, the pore modification agent has a relatively highmelting point, e.g., greater than 60° C., e.g., greater than 75° C., sothat it does not melt during compression of the catalyst precursor intoa slug, tablet, or pellet. Preferably, the pore modification agentcomprises a relatively pure material rather than a mixture. As such,lower melting components will not liquefy under compression duringformation of slugs or tablets. For example, where the pore modificationagent is a fatty acid, lower melting components of the fatty acidmixtures may be removed as liquids by pressing. If this phenomenonoccurs during slug or tablet compression, the flow of liquid may disturbthe pore structure and produce an undesirable distribution of porevolume as a function of pore diameter on the catalyst composition. Inother embodiments, the pore modification agents have a significant vaporpressure at temperatures below their melting points, so that they can beremoved by sublimination into a carrier gas.

For example, the pore modification agent may be a fatty acidcorresponding to the formula CH₃(CH₂)_(x) COOH where x>8. Exemplaryfatty acids include stearic acid (x=16), palmitic acid (x=14), lauricacid (x=10), myristic acid (x=12). The esters of these acids and amidesor other functionalized forms of such acids, for example, stearamide(CH₃(CH₂)₁₆ CONH₂) may also be used. Suitable esters may include methylesters as well as glycerides such as stearin (glycerol tristearate).Mixtures of fatty acids may be used, but substantially pure acids,particularly stearic acid, are generally preferred over mixtures.

In addition, while fatty acids and fatty acid derivatives are generallypreferred, other compositions which meet the functional requirementsdiscussed above are also suitable for use as pore modification agents.Other preferred pore modification agents include but are not limited topolynuclear organic compounds such as naphthalene, graphite, naturalburnout components such as cellulose and its cellulosic derivatives,cellulose-derived materials, such as starches and ground nut shells,such as walnut powder, natural and synthetic oligomers and polymers suchas polyethylene, polyvinyl alcohols and polyacrylic acids and esters.

Catalyst Preparation

In some embodiments where the catalyst is unsupported, the catalystcomposition is formed via a process comprising the step of contacting atitanium salt, a tungsten salt, and (a predetermined amount of) avanadium precursor, e.g., a soluble NH₄VO₃, to form a wet catalystprecursor. Preferably, the process further comprises the step of dryingthe wet catalyst precursor to form a dried catalyst composition. Thedried catalyst composition comprises the components discussed above. Theamounts of the titanium salt, tungsten salt and the vanadium precursorare determined such that the resultant dried catalyst composition has amolar ratio of vanadium to titanium at least 0.02:1, e.g., at least0.05:1, at least 0.10:1, at least 1:1, at least 10:1, at least 30:1, orat least 62.5:1 and a molar ratio of vanadium to tungsten at least0.02:1 e.g., at least 0.05:1, at least 0.10:1, at least 1:1, at least10:1, at least 30:1, or at least 62.5:1.

In one embodiment, the process may further comprise the step of mixingthe vanadium precursor with a reductant solution to form the vanadiumprecursor solution. In one embodiment, the reductant solution maycomprise an acid, silica, water, and/or a glycol. In one embodiment theacid may be an organic acid that may be oxidized by vanadium, e.g., V⁵⁺.In an embodiment, the acid may be selected from the group consisting ofcitric acid, oxalic acid, steric acid, maleic acid, lactic acid,tartaric acid, glycol acid, pyruvic acid, polyacrylic acid and mixturesthereof. In one embodiment, the acid utilized in the reductant solutiondoes not comprise acids that are not oxidized by vanadium, e.g., V⁵⁺,e.g., formic acid, acetic acid, succinic acid, and mixtures thereof. Inan embodiment, the glycol may be selected from the group consisting ofpropylene glycol, ethylene glycol, diethylene glycol, triethyleneglycol, and other polyols. Preferably, the reductant solution comprisesan organic acid, e.g., citric acid and/or oxalic acid, colloidal silica,deionized water, and ethylene glycol. In other embodiments, thereductant solution may also comprise ketones, aldehydes, alcohols, andphenols.

In one embodiment, the formation of the wet catalyst precursor alsoincludes the addition of a binder, which may assist with the formationof pore and/or may improve the strength of the resultant catalystcomposition. Thus, the contacting step may comprise contacting thebinder, e.g., a binder solution, with the titanium salt, the tungstensalt, and/or the vanadium precursor solution to form the wet catalystcomposition. In one embodiment, the binder may be selected from thegroup consisting of cellulose, methyl cellulose, carboxylmethylcellulose, cellulose acetate, cellulose-derived materials, such asstarch, and combinations of two or more of the foregoingpolysaccharides. In one embodiment, oxides, e.g., silica, may beutilized as a binder. In one embodiment, the catalyst compositioncomprises at least 3 wt % of the binder, e.g., at least 5 wt % or atleast 10 wt %. In one embodiment, an acid, e.g., phosphoric acid, may beadded to the wet catalyst composition.

Advantageously, according to one embodiment of the present invention,tungsten precursor is added to the wet catalyst mixture prior tophosphorylation, i.e. addition of phosphoric acid solution. In thismanner, the tungsten is actually incorporated into the metal phosphatematrix of the active phase of the catalyst. It has been found thatadding tungsten prior to phosphorylation of the metals results insignificant improvements in catalytic activity, as compared to eitherconventional V—Ti—P—O catalysts, or even those convention catalystswhich are physically mixed with a tungsten compound, such as WO₃,subsequent to phosphorylation. In one embodiment, the acrylic acid yieldusing the resulting catalyst unexpectedly improved by 30%, as comparedto a reference V—Ti—P—O catalyst without tungsten in the phosphorylatedmatrix.

The process, in one embodiment, may further comprise calcining the driedcatalyst, which, preferably, is conducted in accordance with atemperature profile. As one example, the temperature profile comprisesan increasing stair step temperature profile comprising a plurality ofincreasing hold temperatures. The temperature increases at a rate from1° C. to 10° C. per minute between said hold temperatures. Preferably,the hold temperatures comprise a first, second, third, and fourth holdtemperature. The first hold temperature may range from 150° C. and 300°C., e.g., from 175° C. and 275° C., preferably being about 160° C. Thesecond hold temperature may range from 250° C. and 500° C., e.g., from300° C. and 400° C., preferably being about 250° C. The third holdtemperature may range from 300° C. and 700° C., e.g., from 450° C. and650° C., preferably being about 300° C. The fourth hold temperature mayrange from 400° C. and 700° C., e.g., from 450° C. and 650° C.,preferably being about 450° C. Of course, other temperature profiles maybe suitable. The calcination of the mixture may be done in an inertatmosphere, air or an oxygen-containing gas at the desired temperatures.Steam, a hydrocarbon or other gases or vapors may be added to theatmosphere during the calcination step or post-calcination to causedesired effects on physical and chemical surface properties as well astextural properties such as increase macroporosity.

In one preferred embodiment, the temperature profile comprises:

i) heating the dried catalyst from room temperature to 160° C. at a rateof 10° C. per minute;

ii) heating the dried catalyst composition at 160° C. for 2 hours;

iii) heating the dried catalyst composition from 160° C. to 250° C. at arate of 3° C. per minute;

iv) heating the dried catalyst composition at 250° C. for 2 hours;

v) heating the dried catalyst composition from 250° C. to 300° C. at arate of 3° C. per minute;

vi) heating the dried catalyst composition at 300° C. for 6 hours;

vii) heating the dried catalyst composition from 300° C. to 450° C. at arate of 3° C. per minute; and

viii) heating the dried catalyst composition at 450° C. for 6 hours.

In one embodiment, the catalyst components, e.g., the metal oxidesand/or phosphates precursors, may be physically combined with oneanother to form the catalyst composition. For example the uncalcineddried catalyst components may be ground together and then calcined toform the active catalyst. As another example, the catalyst componentsmay be mixed, milled, and/or kneaded. The catalyst powders formed maythen be calcined to form the final dried catalyst composition.

In one embodiment the phosphorylating agent is added to the mixed metaloxies precursors followed by calcinations.

In one embodiment the catalyst is prepared under hydrothermal conditionsfollowed by calcinations.

In embodiments where the catalyst is supported, the catalystcompositions are formed through metal impregnation of a support(optionally modified support), although other processes such as chemicalgrafting or chemical vapor deposition may also be employed.

In one embodiment, the catalysts are made by impregnating the support,with a solution of the metals or salts thereof in a suitable solvent,followed by drying and optional calcination. Solutions of the modifiersor additives may also be impregnated onto the support in a similarmanner. The impregnation and drying procedure may be repeated more thanonce in order to achieve the desired loading of metals, modifiers,and/or other additives. In some cases, there may be competition betweenthe modifier and the metal for active sites on the support. Accordingly,it may be desirable for the modifier to be incorporated before themetal. Multiple impregnation steps with aqueous solutions may reduce thestrength of the catalyst particles if the particles are fully driedbetween impregnation steps. Thus, it is preferable to allow somemoisture to be retained in the catalyst between successiveimpregnations. In one embodiment, when using non-aqueous solutions, themodifier and/or additive are introduced first by one or moreimpregnations with a suitable non-aqueous solution, e.g., a solution ofan alkoxide or acetate of the modifier metal in an alcohol, e.g.,ethanol, followed by drying. The metal may then be incorporated by asimilar procedure using a suitable solution of a metal compound.

In other embodiments, the modifier is incorporated into the compositionby co-gelling or co-precipitating a compound of the modifier elementwith the silica, or by hydrolysis of a mixture of the modifier elementhalide with a silicon halide. Methods of preparing mixed oxides ofsilica and zirconia by sol gel processing are described by Bosman, etal., in J Catalysis, Vol. 148, (1994), page 660 and by Monros et al., inJ Materials Science, Vol. 28, (1993), page 5832. Also, doping of silicaspheres with boron during gelation from tetraethyl orthosilicate (TEOS)is described by Jubb and Bowen in J Material Science, Vol. 22, (1987),pages 1963-1970. Methods of preparing porous silicas are described inIler R K, The Chemistry of Silica, (Wiley, New York, 1979), and inBrinker C J & Scherer G W Sol-Gel Science published by Academic Press(1990).

The catalyst composition, in some embodiments, will be used in a fixedbed reactor for forming the desired product, e.g., acrylic acid or alkylacrylate. Thus, the catalyst is preferably formed into shaped units,e.g., spheres, granules, pellets, powders, aggregates, or extrudates,typically having maximum and minimum dimensions in the range of 1 to 25mm, e.g., from 2 to 15 mm. Where an impregnation technique is employed,the support may be shaped prior to impregnation. Alternatively, thecomposition may be shaped at any suitable stage in the production of thecatalyst. The catalyst also may be effective in other forms, e.g.powders or small beads and may be used in these forms. In oneembodiment, the catalyst is used in a fluidized bed reactor. In thiscase, the catalyst may be formed using spray dried or spray thermaldecomposition. Preferably, the resultant catalyst has a particle size ofgreater than 300 microns, e.g., greater than 500 microns. In othercases, the catalyst may be prepared via spray drying to form powdersthat can be formed into pellets, extrudates, etc.

Production of Acrylic Acid

In other embodiments, the invention is to a process for producingunsaturated acids, e.g., acrylic acids, or esters thereof (alkylacrylates), by contacting an alkanoic acid with an alkylenating agent,e.g., a methylenating agent, under conditions effective to produce theunsaturated acid and/or acrylate. Preferably, acetic acid is reactedwith formaldehyde in the presence of the inventive catalyst composition.The alkanoic acid, or ester of an alkanoic acid, may be of the formulaR′—CH₂—COOR, where R and R′ are each, independently, hydrogen or asaturated or unsaturated alkyl or aryl group. As an example, R and R′may be a lower alkyl group containing for example 1-4 carbon atoms. Inone embodiment, an alkanoic acid anhydride may be used as the source ofthe alkanoic acid. In one embodiment, the reaction is conducted in thepresence of an alcohol, preferably the alcohol that corresponds to thedesired ester, e.g., methanol. In addition to reactions used in theproduction of acrylic acid, the inventive catalyst, in otherembodiments, may be employed to catalyze other reactions. Examples ofthese other reactions include, but are not limited to butane oxidationto maleic anhydride, acrolein production from formaldehyde andacetaldehyde, and methacrylic acid production from formaldehyde andpropionic acid.

The raw materials, e.g., acetic acid, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from more available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described process may be derived partially or entirely fromsyngas. For example, the acetic acid may be formed from methanol andcarbon monoxide, both of which may be derived from syngas. The syngasmay be formed by partial oxidation reforming or steam reforming, and thecarbon monoxide may be separated from syngas. Similarly, hydrogen thatis used in the step of hydrogenating the acetic acid to form the crudeethanol product may be separated from syngas. The syngas, in turn, maybe derived from variety of carbon sources. The carbon source, forexample, may be selected from the group consisting of natural gas, oil,petroleum, coal, biomass, and combinations thereof. Syngas or hydrogenmay also be obtained from bio-derived methane gas, such as bio-derivedmethane gas produced by landfills or agricultural waste.

In another embodiment, the acetic acid may be formed from thefermentation of biomass. The fermentation process preferably utilizes anacetogenic process or a homoacetogenic microorganism to ferment sugarsto acetic acid producing little, if any, carbon dioxide as a by-product.The carbon efficiency for the fermentation process preferably is greaterthan 70%, greater than 80% or greater than 90% as compared toconventional yeast processing, which typically has a carbon efficiencyof about 67%. Optionally, the microorganism employed in the fermentationprocess is of a genus selected from the group consisting of Clostridium,Lactobacillus, Moorella, Thermoanaerobacter, Propionibacterium,Propionispera, Anaerobiospirillum, and Bacteriodes, and in particular,species selected from the group consisting of Clostridiumformicoaceticum, Clostridium butyricum, Moorella thermoacetica,Thermoanaerobacter kivui, Lactobacillus delbrukii, Propionibacteriumacidipropionici, Propionispera arboris, Anaerobiospirillumsuccinicproducens, Bacteriodes amylophilus and Bacteriodes ruminicola.Optionally in this process, all or a portion of the unfermented residuefrom the biomass, e.g., lignans, may be gasified to form hydrogen thatmay be used in the hydrogenation step of the present invention.Exemplary fermentation processes for forming acetic acid are disclosedin U.S. Pat. Nos. 6,509,180; 6,927,048; 7,074,603; 7,507,562; 7,351,559;7,601,865; 7,682,812; and 7,888,082, the entireties of which areincorporated herein by reference. See also U.S. Pub. Nos. 2008/0193989and 2009/0281354, the entireties of which are incorporated herein byreference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. U.S. Pat. No.5,821,111, which discloses a process for converting waste biomassthrough gasification into synthesis gas, and U.S. Pat. No. 6,685,754,which discloses a method for the production of a hydrogen-containing gascomposition, such as a synthesis gas including hydrogen and carbonmonoxide, are incorporated herein by reference in their entireties.

The acetic acid fed to the hydrogenation reactor may also comprise othercarboxylic acids and anhydrides, as well as aldehyde and/or ketones,such as acetaldehyde and acetone. Preferably, a suitable acetic acidfeed stream comprises one or more of the compounds selected from thegroup consisting of acetic acid, acetic anhydride, acetaldehyde, ethylacetate, and mixtures thereof. These other compounds may also behydrogenated in the processes of the present invention. In someembodiments, the presence of carboxylic acids, such as propanoic acid orits anhydride, may be beneficial in producing propanol. Water may alsobe present in the acetic acid feed.

Methanol carbonylation processes suitable for production of acetic acidare described in U.S. Pat. Nos. 7,208,624; 7,115,772; 7,005,541;6,657,078; 6,627,770; 6,143,930; 5,599,976; 5,144,068; 5,026,908;5,001,259 and 4,994,608, all of which are hereby incorporated byreference.

In one optional embodiment, the acetic acid that is utilized in thecondensation reaction comprises acetic acid and may also comprise othercarboxylic acids, e.g., propionic acid, esters, and anhydrides, as wellas acetaldehyde and acetone. In one embodiment, the acetic acid fed tothe hydrogenation reaction comprises propionic acid. For example thepropionic acid in the acetic acid feed stream may range from 0.001 wt %to 15 wt %, e.g., from 0.125 wt % to 12.5 wt %, from 1.25 wt % to 11.25wt %, or from 3.75 wt % to 8.75 wt %. Thus, the acetic acid feed streammay be a cruder acetic acid feed stream, e.g., a less-refined aceticacid feed stream.

As used herein, “alkylenating agent” means an aldehyde or precursor toan aldehyde suitable for reacting with the alkanoic acid, e.g., aceticacid, in an aldol condensation reaction to form an unsaturated acid,e.g., acrylic acid, or an alkyl acrylate. In preferred embodiments, thealkylenating agent comprises a methylenating agent such as formaldehyde,which preferably is capable of adding a methylene group (═CH₂) to theorganic acid. Other alkylenating agents may include, for example,acetaldehyde, propanal, and butanal.

The alkylenating agent, e.g., formaldehyde, may be added from anysuitable source. Exemplary sources may include, for example, aqueousformaldehyde solutions, anhydrous formaldehyde derived from aformaldehyde drying procedure, trioxane, diether of methylene glycol,and paraformaldehyde. In a preferred embodiment, the formaldehyde isproduced via a formox unit, which reacts methanol and oxygen to yieldthe formaldehyde.

In other embodiments, the alkylenating agent is a compound that is asource of formaldehyde. Where forms of formaldehyde that are not asfreely or weakly complexed are used, the formaldehyde will form in situin the condensation reactor or in a separate reactor prior to thecondensation reactor. Thus for example, trioxane may be decomposed overan inert material or in an empty tube at temperatures over 350° C. orover an acid catalyst at over 100° C. to form the formaldehyde.

In one embodiment, the alkylenating agent corresponds to Formula I.

In this formula, R₅ and R₆ may be independently selected from C₁-C₁₂hydrocarbons, preferably, C₁-C₁₂ alkyl, alkenyl or aryl, or hydrogen.Preferably, R₅ and R₆ are independently C₁-C₆ alkyl or hydrogen, withmethyl and/or hydrogen being most preferred. X may be either oxygen orsulfur, preferably oxygen; and n is an integer from 1 to 10, preferably1 to 3. In some embodiments, m is 1 or 2, preferably 1.

In one embodiment, the compound of formula I may be the product of anequilibrium reaction between formaldehyde and methanol in the presenceof water. In such a case, the compound of formula I may be a suitableformaldehyde source. In one embodiment, the formaldehyde source includesany equilibrium composition. Examples of formaldehyde sources includebut are not restricted to methylal(1,1 dimethoxymethane);polyoxymethylenes —(CH₂—O)_(i)— wherein i is from 1 to 100; formalin;and other equilibrium compositions such as a mixture of formaldehyde,methanol, and methyl propionate. In one embodiment, the source offormaldehyde is selected from the group consisting of 1,1dimethoxymethane; higher formals of formaldehyde and methanol; andCH₃—O—(CH₂—O)_(i)—CH₃ where i is 2.

The alkylenating agent may be used with or without an organic orinorganic solvent.

The term “formalin,” refers to a mixture of formaldehyde, methanol, andwater. In one embodiment, formalin comprises from 25 wt % to 85 wt %formaldehyde; from 0.01 wt % to 25 wt % methanol; and from 15 wt % to 70wt % water. In cases where a mixture of formaldehyde, methanol, andmethyl propionate is used, the mixture comprises less than 10 wt %water, e.g., less than 5 wt % or less than 1 wt %.

In some embodiments, the condensation reaction may achieve favorableconversion of acetic acid and favorable selectivity and productivity toacrylate product(s). For purposes of the present invention, the term“conversion” refers to the amount of acetic acid in the feed that isconverted to a compound other than acetic acid. Conversion is expressedas a mole percentage based on acetic acid in the feed. The overallconversion of acetic acid may be at least 15 mol %, e.g., at least 25mol %, at least 40 mol %, or at least 50 mol %. In another embodiment,the reaction may be conducted wherein the molar ratio of acetic acid toalkylenating agent is at least 0.50:1, e.g., at least 1:1.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 30 mol % of the converted acetic acidis converted to acrylic acid, the acrylic acid selectivity would be 30mol %. Preferably, the catalyst selectivity to acrylate product, e.g.,acrylic acid and methyl acrylate, is at least 30 mol %, e.g., at least50 mol %, at least 60 mol %, or at least 70 mol %. In some embodiments,the selectivity to acrylic acid is at least 30 mol %, e.g., at least 40mol %, or at least 50 mol %; and/or the selectivity to methyl acrylateis at least 10 mol %, e.g., at least 15 mol %, or at least 20 mol %.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., acrylate product(s), formed during thecondensation based on the liters of catalyst used per hour. Aproductivity of at least 20 grams of acrylates per liter catalyst perhour, e.g., at least 40 grams of acrylates per liter catalyst per houror at least 100 grams of acrylates per liter catalyst per hour, ispreferred. In terms of ranges, the productivity preferably is from 20 to800 grams of acrylates per liter catalyst per hour, e.g., from 100 to600 per kilogram catalyst per hour or from 200 to 400 per kilogramcatalyst per hour.

As noted above, the inventive catalyst composition provides for highconversions of acetic acid. Advantageously, these high conversions areachieved while maintaining selectivity to the desired acrylateproduct(s), e.g., acrylic acid and/or methyl acrylate. As a result,acrylate product productivity is improved, as compared to conventionalproductivity with conventional catalysts.

Preferred embodiments of the inventive process also have low selectivityto undesirable products, such as carbon monoxide and carbon dioxide. Theselectivity to these undesirable products preferably is less than 30%,e.g., less than 20% or less than 10%. More preferably, these undesirableproducts are not detectable. Formation of alkanes, e.g., ethane, may below, and ideally less than 2%, less than 1%, or less than 0.5% of theacetic acid passed over the catalyst is converted to alkanes, which havelittle value other than as fuel.

The alkanoic acid or ester thereof and alkylenating agent may be fedindependently or after prior mixing to a reactor containing thecatalyst. The reactor may be any suitable reactor. Preferably, thereactor is a fixed bed reactor, but other reactors such as a continuousstirred tank reactor or a fluidized bed reactor, may be used.

In some embodiments, the alkanoic acid, e.g., acetic acid, and thealkylenating agent, e.g., formaldehyde, are fed to the reactor at amolar ratio of at least 0.25:1, e.g., at least 0.75:1 or at least 1:1.In terms of ranges the molar ratio of alkanoic acid to alkylenatingagent may range from 0.50:1 to 10:1 or from 0.75:1 to 5:1. In someembodiments, the reaction of the alkanoic acid and the alkylenatingagent is conducted with a stoichiometric excess of alkanoic acid. Inthese instances, acrylate selectivity may be improved. As an example theacrylate selectivity may be at least 10% higher than a selectivityachieved when the reaction is conducted with an excess of alkylenatingagent, e.g., at least 20% higher or at least 30% higher. In otherembodiments, the reaction of the alkanoic acid and the alkylenatingagent is conducted with a stoichiometric excess of alkylenating agent.

The condensation reaction may be conducted at a temperature of at least250° C., e.g., at least 300° C., or at least 350° C. In terms of ranges,the reaction temperature may range from 200° C. to 500° C., e.g., from300° C. to 400° C., or from 350° C. to 390° C. Reaction pressure is notparticularly limited, and the reaction is typically performed nearatmospheric pressure. In one embodiment, the reaction may be conductedat a pressure ranging from 0 kPa to 4100 kPa, e.g., from 3 kPa to 345kPa, or from 6 kPa to 103 kPa.

Water may be present in amounts up to 60 wt %, by weight of the reactionmixture, e.g., up to 50 wt % or up to 40 wt %. Water, however, ispreferably reduced due to its negative effect on process rates andseparation costs.

In one embodiment, an inert or reactive gas is supplied to the reactantstream. Examples of inert gases include, but are not limited to,nitrogen, helium, argon, and methane. Examples of reactive gases orvapors include, but are not limited to, oxygen, carbon oxides, sulfuroxides, and alkyl halides. When reactive gases such as oxygen are addedto the reactor, these gases, in some embodiments, may be added in stagesthroughout the catalyst bed at desired levels as well as feeding withthe other feed components at the beginning of the reactors.

In one embodiment, the unreacted components such as the carboxylic acidand formaldehyde as well as the inert or reactive gases that remain arerecycled to the reactor after sufficient separation from the desiredproduct.

When the desired product is an unsaturated ester made by reacting anester of an alkanoic acid ester with formaldehyde, the alcoholcorresponding to the ester may also be fed to the reactor either with orseparately to the other components. For example, when methyl acrylate isdesired, methanol may be fed to the reactor. The alcohol, amongst othereffects, reduces the quantity of acids leaving the reactor. It is notnecessary that the alcohol is added at the beginning of the reactor andit may for instance be added in the middle or near the back, in order toeffect the conversion of acids such as propionic acid, methacrylic acidto their respective esters without depressing catalyst activity.

EXAMPLES Example 1

Catalyst compositions were prepared using a tungsten salt, a titaniumsalt, and a vanadium precursor, e.g., NH₄VO₃. An aqueous suspension ofTiP₂O₇ was prepared by adding the finely powdered solid to 50 mL ofdeionized H₂O, Next, a calculated amount of phosphoric acid (85%) wasadded, the suspension heated to 80° C. with stifling and kept at thistemperature for 30 min. Separately, an organic acid, e.g., oxalic acidor citric acid, was added was dissolved in deionized H₂O, and thesolution was heated to about 50° C. with stifling. Next, calculatedamounts of NH₄VO₃ and ammonium metatungstate hydrate were added in smallportion over about 10 min, the solution was then heated to 80° C. withstirring, and kept at this temperature for 60 min. Next, the darkblue-green solution was then added to the suspension of TiP₂O₇ withstirring, and the final mixture was kept stirring for another 30 min atthis temperature. The final mixture was then evaporated to dryness(rotary evaporator), and the resulting solid is dried (120° C.)overnight/air and calcined using the following temperature program:

(1) heating to 160° C. at a rate of 10° C. per minute, and holding at160° C. for 2 hours;

(2) heating to 250° C. at a rate of 3° C. per minute, and holding at250° C. for 2 hours;

(3) heating to 300° C. at a rate of 3° C. per minute, and holding at300° C. for 6 hours; and

(4) heating to 450° C. at a rate of 3° C. per minute, and holding at450° C. for 6 hours.

Example 2

Colloidal silica and deionized water were combined and mixed. Ti(OiPr)₄was mixed with iPrOH and this mixture was added to the water-colloidalsilica mixture and stirred at room temperature for at least 30 minutes.Separately, an organic acid, e.g., oxalic acid or citric acid andethylene glycol and water were combined, and was heated to 50° C. Acalculated amount of NH₄VO₃ was added to the mixture and the resultingsolution was heated to 80° C. with stirring. A calculated amount ofammonium metatungstate was added to the warm vanadium solution and wasstirred for 15 minutes at 80° C. Optionally, a solution of methylcellulose was added to the vanadium and tungsten mixture. The mixturewas stirred at 80° C. for 15-30 minutes. The vanadium/tungsten mixturewas cooled and was slowly added to the titania suspension/gel. Themixture was stirred for at least 15 minutes at room temperature. Acalculated amount of phosphoric acid (85%) was added and the resultingsolution was stirred. The final mixture was evaporated to dryness in a120° C. drying oven overnight. The resulting solid was calcined usingthe temperature profile of Example 1.

The effect of vanadium, tungsten and/or titanium on the surface area,pore volume, and pore size of the resultant catalyst was studied.Catalysts 1 and 2 were prepared using citric acid as detailed in Example2. Table 2 shows surface area, pore volume, and pore size of Catalysts 1and 2. Catalyst 1 has a V:W:Ti ratio of 6.12:0.87:4 and Catalyst 2 has aV:W:Ti ratio of 1.75:0.25:4.

As shown in Table 2, Catalyst 1 has a 3.5 times more vanadium andtungsten than Catalyst 2.

TABLE 2 Catalyst Compositions Catalyst Catalyst Formula PreparationDetails 1 V_(6.12)W_(0.87)Ti₄P₁₆O₆₂ citric acid, ethylene glycol, 5.8%SiO₂ 2 V_(1.75)W_(0.25)Ti₄P₁₁O₄₀ citric acid, ethylene glycol, 5.8% SiO₂

Example 3

A reaction feed comprising acetic acid, formaldehyde, methanol, water,oxygen, and nitrogen was passed through a fixed bed reactor comprisingCatalysts 1-2 shown in Table 2. The reactions for Catalysts 1-2 wereconducted at a reactor temperature of 375° C. and a GHSV of 2000 Hr⁻¹,total organics of 32 mole %, acetic acid and formaldehyde ratio of 1.5,O₂ of 4.8%, H₂O of 7.2 mole %, total N₂ of 56 mole %, and formalin wasfed as trioxane. Acrylic acid and methyl acrylate (collectively,“acrylate product”) were produced. Acetic acid conversion, acrylateselectivity, acrylate yield, and acrylate space time yield were measuredfor Catalysts 1-3 a various time points of the reaction. Commercial VPOcatalyst Comp. A and Comp. B were also tested under the same condition.The results are shown in Table 3.

TABLE 3 Acrylate Production HOAc Acrylate Acrylate Acrylate RuntimeConv. Selectivity Yield STY Catalyst (h) (%) (%) (%) (g/hr/L) 1 0.5 4785 40 517 1.5 46 85 39 509 2.5 46 86 40 515 3.1 45 86 39 506 17.4 42 8435 462 19.4 42 84 35 456 20.3 40 88 35 462 2 0.5 35 83 29 384 1.5 35 8329 377 2.5 35 83 29 382 3.1 35 82 28 371 17.4 32 81 26 345 18.4 33 81 26345 19.4 33 80 26 345 20.3 33 81 27 350 VPO 0.8 27 85 23 304 Comp. A 1.724 94 22 289 2.7 23 95 22 280 3.9 22 97 21 277 VPO 0.8 22 90 20 255Comp. B 1.7 22 90 19 253 2.7 22 87 19 251 3.9 22 90 19 254

Acetic acid conversion, acrylate selectivity, acrylate yield, andacrylate space time yield were measured for Catalysts 1 and 2 and Comp.A and Comp. B at various time points of the reaction. Comp. A is acommercially available VPO catalyst and Comp. B was prepared usingcitric acid, ethylene glycol, silica and 10% methyl cellulose. Catalysts1 and 2, both of which contain vanadium, tungsten and titanium,unexpectedly outperform Comp. A and Comp. B, which are conventionaltungsten-free and titanium-free commercially available vanadiumcatalysts. Catalysts 1 and 2 show better acetic acid conversions,acrylate yield, and acrylate STY than Comp. A and Comp. B. Specifically,Catalysts 1 and 2 show initial acetic acid conversion of 47% and 35%,respectively. In comparison, Comp. A and Comp. B show an initial aceticacid conversion of 27% and 22%, respectively.

Furthermore, surprisingly Catalysts 1 and 2 maintained steady aceticacid conversion, acrylate selectivity, acrylate yield, and acrylatespace time yield over long time periods, i.e., Catalysts 1 and 2 showedlittle if any catalyst deactivation. For example, Catalyst 1 has aninitial acetic acid conversion of 47% and reduces to 40% over the courseof 20.3 hours; and Catalyst 2 has an initial acetic acid conversion of35% and slightly reduces to 33% over 20.3 hours. In comparison, Comp. Ahas an initial acetic acid conversion of 27% and decreases to 22% overonly 3.9 hours. Therefore, as shown by the data, Catalysts 1 and 2outperform commercially available VPO catalyst.

Example 4

Table 4 shows Catalysts 3-8, each of which are VWTiPO catalysts preparedvia the preparation method of Example 2.

TABLE 4 Catalyst Compositions Catalyst Catalyst Formula PreparationDetails 3 V₁₀W_(1.0)Ti₄P_(20.2)O₈₄ oxalic acid, ethylene glycol, 8.3%SiO₂ 4 V₁₀W_(0.16)Ti₆P_(24.4)O₉₆ oxalic acid, ethylene glycol, 8.0% SiO₂5 V₁₀W_(1.0)Ti₄P_(20.2)O₈₄ oxalic acid, ethylene glycol, 8.5% SiO₂, 10%MC 6 V₁₀W_(1.0)Ti₄P_(20.2)O₈₄ citric acid, ethylene glycol, 5.8% SiO₂,10% MC 7 V₁₀W_(0.16)Ti₄P_(20.1)O₈₁ citric acid, ethylene glycol, 5.8%SiO₂, 10% MC 8 V₁₀W_(0.16)Ti₁₀P₃₃O₁₂₈ citric acid, ethylene glycol, 5.8%SiO₂, 10% MC

Catalysts 3-5 were made using oxalic acid and between 8.0 to 8.5% SiO₂.Catalysts 6-8 were made using citric acid and 5.8% SiO₂. Catalysts 5-8also included 10% methyl cellulose whereas catalysts 3 and 4 were freeof methyl cellulose. Catalysts 3, 5, and 6 have V:W:Ti ratio of10:1.0:4. Catalyst 4 has a V:W:Ti ratio of 10:0.16:6. Catalyst 7 has aV:W:Ti ratio of 10:0.16:4. Catalyst 8 has a V:W:Ti ratio of 10:0.16:10.

Example 5

A reaction feed comprising acetic acid, formaldehyde, methanol, water,oxygen, and nitrogen was passed through a fixed bed reactor comprisingCatalysts 3-8 shown in Table 4. The reactions for Catalysts 3-8 wereconducted at a reactor temperature of 375° C. and a GHSV of 2000 Hr⁻¹,total organics of 32 mole %, acetic acid and formaldehyde ratio of 1.5,O₂ of 4.8%, H₂O of 7.2 mole %, total N₂ of 56 mole %, and formalin wasfed as trioxane. Acrylic acid and methyl acrylate (collectively,“acrylate product”) were produced. Acetic acid conversion, acrylateselectivity, acrylate yield, and acrylate space time yield were measuredfor Catalysts 3-8 at various time points of the reaction. A commercialVPO catalyst Comp. A was also tested under the same condition. Theresults are shown in Table 5.

TABLE 5 Acrylate Production HOAc Acrylate Acrylate Acrylate RuntimeConv. Selectivity Yield STY Catalyst (h) (%) (%) (%) (g/hr/L) 3 0.5 2781 22 287 1.4 28 81 22 296 2.0 28 82 23 303 16.3 28 81 23 303 17.3 28 8123 305 18.0 28 81 23 304 Avg. 28 81 23 300 4 0.5 30 88 26 348 1.4 32 8928 369 2.0 32 89 28 373 16.3 34 87 29 387 17.3 34 88 30 396 18.0 34 8830 393 Avg. 33 88 29 378 5 0.5 35 90 31 409 1.5 35 90 31 409 2.7 35 9031 410 3.8 35 89 31 408 22.4 36 90 32 422 23.6 35 93 33 430 24.7 35 9533 435 25.7 37 87 32 421 Avg. 35 90 32 418 6 0.5 37 84 31 406 1.5 35 8430 394 2.3 35 84 29 388 17.1 36 83 30 391 18.3 35 84 30 392 19.3 35 8329 389 Avg. 36 84 30 393 7 2.3 30 82 24 323 3.5 30 83 25 328 17.1 30 8224 323 18.4 29 83 25 326 19.6 29 82 24 320 Avg. 30 83 24 324 8 0.7 26 8622 297 1.6 27 85 23 300 2.4 27 86 24 311 17.5 30 83 25 336 18.6 31 85 26345 19.8 31 83 26 340 Avg. 29 85 24 321 VPO 0.8 27 85 23 304 Comp. A 1.724 94 22 289 2.7 23 95 22 280 3.9 22 97 21 277 Avg. 24 93 22 287

Catalysts 3-8, all of which contain vanadium, tungsten and titanium,unexpectedly outperform Comp. A, which is conventional tungsten-free andtitanium-free commercially available catalysts. For example, Catalysts3-8 demonstrate average acetic acid conversions of 28%, 33%, 35%, 36%,30%, and 39%, respectively, while Comp. A demonstrates an average aceticacid conversion of only 24%. Also, Catalysts 3-8 demonstrate averageacrylate STY of 300 g/hr/L, 378 g/hr/L, 418 g/hr/L, 393 g/hr/L, 324g/hr/L, and 321 g/hr/L, respectively, while Comp. A demonstrates anaverage STY of only 287 g/hr/L. In addition, Catalysts 3-8 demonstrateaverage acrylate yields of 23%, 29%, 32%, 30%, 24% and 24%,respectively, while Comp. A demonstrates an average yield of only 22%.

Surprisingly and unexpectedly, as shown, all catalysts maintained steadyor increase acetic acid conversion, acrylate selectivity, acrylateyield, and acrylate space time yield over long time periods, i.e.,Catalysts 3-8 showed little if any catalyst deactivation. For example,over a 18.0 hour period, the acetic acid conversion for Catalyst 3remains between 27% and 28%. Over a 18.0 hour period, the acetic acidconversion for Catalyst 4 increases from 30% to 34%. Similarly, over a25.7 hour period, the acetic acid conversion for Catalyst 5 remainsbetween 35% and 37%. In addition, over a 18.0 hour period, the aceticacid conversion for Catalyst 6 remains between 35% to 37%. Similarly,over a 19.6 hour period, the acetic acid conversion for Catalyst 7remains between 29% to 30%. Over a 19.8 hour period, the acetic acidconversion for Catalyst 8 increases from 26% to 31%.

In comparison, acetic acid conversion for Comp. A decreasedsignificantly from 27% to 22% within only 3.9 hours

As shown in Table 5, Catalysts 3-8 have steady acrylate yield andacrylate space time yield. For example, Catalyst 3 has an acrylate yieldbetween 22% to 23% and acrylate space time yield between 287 g/hr/L and305 g/hr/L. Catalyst 4 has an acrylate yield between 26% to 30% andacrylate space time yield increase from 348 g/hr/L to 396 g/hr/L.Catalyst 5 has an acrylate yield between 31% to 33% and acrylate spacetime yield between 408 g/hr/L and 435 g/hr/L. Catalyst 6 has an acrylateyield between 29% to 31% and acrylate space time yield between 388g/hr/L and 406 g/hr/L. Catalyst 7 has an acrylate yield between 24% to25% and acrylate space time yield between 320 g/hr/L and 328 g/hr/L.Catalyst 8 has an acrylate yield between 22% to 26% and acrylate spacetime yield between 297 g/hr/L and 345 g/hr/L.

Therefore, as shown by the data, Catalysts 3-8, which comprise vanadium,tungsten, and titanium outperform commercially available VPO catalyst.

Example 6

Table 6 shows Catalysts 9-12, each of which are VWTiPO catalystsprepared via the preparation method of Example 2.

TABLE 6 Catalyst Compositions Catalyst Catalyst Formula PreparationDetails 9 V₁₀W_(1.0)Ti_(0.16)P_(11.9)O₅₅ oxalic acid, ethylene glycol,8.2% SiO₂ 10 V₁₀W_(1.0)Ti_(0.16)P_(11.9)O₅₅ oxalic acid, ethyleneglycol, 8.6% SiO₂, 10% MC 11 V₁₀W_(1.0)Ti_(0.16)P_(11.9)O₅₅ citric acid,ethylene glycol, 5.8% SiO₂, 10% MC 12 V₁₀W_(0.16)Ti_(0.16)P_(11.6)O₅₅citric acid, ethylene glycol, 5.8% SiO₂, 10% MC

Catalysts 9 and 10 were made using oxalic acid, ethylene glycol, and8.2% and 8.5% SiO₂, respectively. Catalysts 11 and 12 were made usingcitric acid, ethylene glycol, and 5.8% SiO₂. Catalysts 10-12 alsoincluded 10% methyl cellulose whereas Catalyst 9 was free of methylcellulose. Catalysts 9, 10, and 11 have V:W:Ti ratio of 10:1.0:0.16.Catalyst 12 has a V:W:Ti ratio of 10:0.16:0.16.

Example 7

A reaction feed comprising acetic acid, formaldehyde, methanol, water,oxygen, and nitrogen was passed through a fixed bed reactor comprisingCatalysts 9-12 shown in Table 6. The reactions for Catalysts 9-12 wereconducted at a reactor temperature of 375° C. and a GHSV of 2000 Hr⁻¹,total organics of 32 mole %, acetic acid and formaldehyde ratio of 1.5,O₂ of 4.8%, H₂O of 7.2 mole %, total N₂ of 56 mole %, and formalin wasfed as trioxane. Acrylic acid and methyl acrylate (collectively,“acrylate product”) were produced. Acetic acid conversion, acrylateselectivity, acrylate yield, and acrylate space time yield were measuredfor Catalysts 9-12 at various time points of the reaction. A commercialVPO catalyst Comp. A was also tested under the same condition. Theresults are shown in Table 7.

TABLE 7 Acrylate Production HOAc Acrylate Acrylate Acrylate RuntimeConv. Selectivity Yield STY Catalyst (h) (%) (%) (%) (g/hr/L)  9 0.5 2088 18 234 1.5 21 88 18 238 2.3 21 87 18 240 17.1 21 86 18 239 18.3 21 8719 244 19.3 21 87 18 241 Avg. 21 87 18 239 10 0.5 33 87 29 383 1.5 33 8729 386 2.7 34 87 29 388 3.8 34 87 29 390 22.4 34 85 29 387 23.6 34 86 29389 24.7 35 85 29 390 25.7 34 85 29 387 Avg. 34 86 29 388 11 2.3 44 8035 454 3.5 44 81 35 455 17.1 43 80 34 442 18.4 43 81 35 451 19.6 43 8135 450 Avg. 43 81 35 450 12 0.7 28 86 24 318 1.6 28 87 25 324 2.4 28 8725 325 17.5 28 85 24 312 18.6 28 86 24 314 19.8 28 86 24 313 Avg. 28 8624 318 VPO 0.8 27 85 23 304 Comp. A 1.7 24 94 22 289 2.7 23 95 22 2803.9 22 97 21 277 Avg. 24 93 22 287

Catalysts 9-12, all of which contain vanadium, tungsten and titanium,unexpectedly outperform Comp. A, which is conventional tungsten-free andtitanium-free VPO catalysts. For example, Catalysts 10-13 demonstrateaverage acetic acid conversions of 21%, 34%, 43%, and 28%, respectively,while Comp. A demonstrates average acetic acid conversion of only 24%.Also, Catalysts 9-12 demonstrate average acrylate STY of 239 g/hr/L, 388g/hr/L, 450 g/hr/L, and 318 g/hr/L, respectively, while Comp. Ademonstrates an average yield of only 287 g/hr/L. In addition, Catalysts9-12 demonstrate average acrylate yields of 18%, 29%, 33%, and 24%,respectively, while Comp. A demonstrates average yield of only 22%.

Surprisingly and unexpectedly, as shown, all catalysts maintained steadyor increase acetic acid conversion, acrylate selectivity, acrylateyield, and acrylate space time yield over long time periods, i.e.,Catalysts 9-12 showed little if any catalyst deactivation. For example,over a 19.3 hour period, the acetic acid conversion for Catalyst 9remains between 20% and 21%. Over a 25.7 hour period, the acetic acidconversion for Catalyst 10 remains between 33% and 34%. Similarly, overa 19.6 hour period, the acetic acid conversion for Catalyst 11 remainsbetween 44% and 43%. In addition, over a 19.8 hour period, the aceticacid conversion for Catalyst 12 remains at 28%. In comparison, aceticacid conversion of Comp. A decreases significantly from 27% to 22%within only 3.9 hours.

It appears that catalysts with a low level of titanium have similar orbetter acetic acid conversion and acrylate STY than commerciallyavailable VPO catalysts. For example, Catalysts 9-11 have steadyacrylate yield and acrylate space time yield. For example, Catalyst 9has a steady acrylate yield of 18% and acrylate space time yield between234 g/hr/L and 244 g/hr/L. Catalyst 10 has a steady acrylate yield of29% and acrylate space time yield between 383 g/hr/L and 390 g/hr/L.Catalyst 11 has an acrylate yield between 34% to 35% and acrylate spacetime yield between 442 g/hr/L and 455 g/hr/L.

Surprisingly and unexpectedly, it appears that catalyst with low levelof titanium and tungsten has similar or better acetic acid conversionand acrylate STY than commercially available VPO catalysts. For example,Catalyst 12 has a steady acrylate yield between 24% and 25% and acrylatespace time yield between 312 g/hr/L and 325 g/hr/L.

Therefore, as shown by the data, Catalysts 9-12, which comprisevanadium, tungsten, and titanium outperform commercially available VPOcatalyst.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited below and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing an acrylate product, the processcomprising the steps of: (a) contacting an alkanoic acid and analkylenating agent over a catalyst under conditions effective to producethe acrylate product, (b) wherein the catalyst comprises vanadium,titanium and tungsten.
 2. The process of claim 1, wherein molar ratio ofvanadium to tungsten ranges from 0.02:1 to 1000:1.
 3. The process ofclaim 1, wherein an overall alkanoic acid conversion is at least 15 mol%.
 4. The process of claim 1, wherein a space time yield of thecombination of acrylic acid and acrylates is at least 50 grams/hr/1 ofcatalyst.
 5. A process for producing a catalyst composition, the processcomprising the steps of: (a) contacting a titanium precursor, a vanadiumprecursor, and a tungsten precursor to form a catalyst precursormixture, and (b) calcining the catalyst precursor mixture to form adried catalyst composition comprising titanium, vanadium, and tungsten.6. The process of claim 5, wherein the dried catalyst composition has anmolar ratio of vanadium to tungsten ranging from 0.02:1 to 1000:1. 7.The process of claim 5, wherein the vanadium precursor is NH₄VO₃,wherein the tungsten precursor is ammonium metatungstate hydrate, andwherein the titanium precursor is TiP₂O₇.
 8. The process of claim 5,wherein step (a) comprises: contacting the vanadium precursor and atungsten precursor with a reductant, to form a vanadium/tungstenprecursor mixture or a vanadium/tungsten precursor mixture; contactingthe titanium precursor and phosphoric acid, to form a titanium precursormixture; and contacting the titanium precursor mixture with thevanadium/tungsten precursor mixture to form wet catalyst precursormixture.
 9. The process of claim 5, wherein said contacting furthercomprises contacting one or more of said titanium precursor, vanadiumprecursor, tungsten precursor and wet catalyst precursor mixture with anadditive selected from the group consisting of molding assistants,reinforcements, pore-forming or pore modification agents, binders,stearic acid, graphite, starch, methyl cellulose, and glass fibers. 10.The process of claim 5, wherein said additive is either methyl celluloseor a binder.
 11. The process of claim 5, further comprising depositingsaid wet catalyst mixture onto a support selected from the groupconsisting of silica, alumina, zirconia, titania, aluminosilicates,zeolitic materials, sintered metal supports, ceramic foams, metal forms,honeycombed monoliths, formed metal foils and mixtures thereof.
 12. Acatalyst composition, comprising an active phase comprising: vanadium,titanium, and tungsten, wherein the catalyst composition is suitable foruse in an aldol condensation of an alkanoic acid and an alkylenatingagent to form an acrylate product.
 13. The catalyst composition of claim12, wherein molar ratio of vanadium to tungsten in the active phase ofthe catalyst composition ranges from 0.02:1 to 1000:1.
 14. The catalystcomposition of claim 12, wherein the active phase further comprisesphosphorus.
 15. The catalyst composition of claim 12, wherein the activephase comprises from 0.2 wt % to 30 wt % vanadium.
 16. The catalystcomposition of claim 12, wherein the active phase comprises from 0.016wt % to 20 wt % titanium.
 17. The catalyst composition of claim 12,wherein the active phase comprises from 0.11 wt % to 65 wt % tungsten.18. The catalyst composition of claim 12, further comprises a supportselected from the group consisting of silica, alumina, zirconia,titania, aluminosilicates, zeolitic materials, sintered metal supports,ceramic foams, metal forms, honeycombed monoliths, formed metal foilsand mixtures thereof.
 19. The catalyst composition of claim 12, whereinthe catalyst composition further comprises an additive selected from thegroup consisting of molding assistants, reinforcements, pore-forming orpore modification agents, binders, stearic acid, graphite, starch,cellulose, and glass fibers.
 20. The catalyst composition of claim 12,wherein the catalyst composition further comprises methyl cellulose. 21.The catalyst composition of claim 12, wherein the catalyst correspondsto the formulaV_(a)Ti_(b)W_(c)P_(d)O_(e), wherein: a is from 1 to 100, b is from 0.1to 50, c is from 0.1 to 50, d is from 1 to 270, e is from 6 to 1040.